Can radiation therapy be used to prevent scar tissue regrowth?

Yes. Keloids are hypertrophic or very thick scars in predisposed patients who form them. They must be excised and the new incision radiated to prevent the keloid. Treating a keloid as is does not get rid of it or shrink it with radiation.
Yes. Radiation can be used to treat keloids. It is most commonly done right after (i.e. The same day) as the surgical removal of the keloid.

Related Questions

Can healthy people get radiation therapy to prevent cancer?

No. We can not take unnecessary radiation as it has it's risk and would give no benefit. However we all get very very low amounts of radiation from the earth and atmosphere. This keeps our bodies repair systems for any damage radiation causes functional. However if we never got any radiation that is what would be best. Radiation therapy is only needed for cancer and other benign conditions. Read more...
No. Healthy people have more risk than beneft from exposure to radiotherapy or radiation from any source. Read more...

Are things like radiation therapy, 5-fluorouracil, or interferon (IFN) therapy safe hypertrophic scar treatments or over the top? Other options?

Scar treatment. Nothing is "over the top", if you have done the appropriate therapies and aren't getting the results you want. You should always consider the risk/benefit ratio for anything you contemplate doing. Read more...